Adverse Events From Supplements Merit Scrutiny

The observed increase in heart problems also may be related to low levels of vitamin D and vitamin K, which play a role in calcium metabolism and bone formation, he suggested.

“This study is an alert, not absolute proof, and the finding has not shown up in other calcium studies. So it is not appropriate to conclude that calcium is causing the problem. Do not dissuade patients from taking calcium, but don't overdo it: 1,200 mg/day is fine.” He added that it's a very good idea to make sure patients are also getting enough magnesium.

▸ Selenium and type 2 diabetes. Selenium has been recommended as a possible preventive for several different conditions, including Alzheimer's disease, prostate cancer (though its merits in this context were challenged by the Selenium and Vitamin E Cancer Prevention Trial [SELECT]), and type 2 diabetes. The latter recommendation is based on epidemiologic data showing a strong inverse correlation between incidence of diabetes and selenium intake.

But a secondary analysis of data from the Nutritional Prevention of Cancer Trial indicated that individuals taking 200 mcg of supplemental selenium daily had a significant increase of type 2 diabetes over an 8-year period (Ann. Intern. Med. 2007;147:217–23).

This unexpected finding was corroborated by SELECT, which also showed an increased rate of diabetes in those taking selenium alone, though the difference was not statistically significant.

Complicating matters, there was no diabetes increase in SELECT among patients taking selenium plus vitamin E, compared with those taking placebo. In fact, the incidence actually went down slightly, though, again, the difference was not significant.

“When selenium is taken by itself, it may be oxidative rather than antioxidative. So taking high doses of selenium or any other independent antioxidant may not be so healthy,” Dr. Gregory hypothesized. He added that selenium may also stimulate glucagon release.

Though the picture is hardly clear, he advised against recommending selenium alone, especially for individuals prone to insulin resistance and diabetes. “The diabetes finding is a signal. We can't draw definitive conclusions from it, but we do need to be aware of it,” he concluded.

Dr. Gregory reported having no financial conflicts of interest related to his presentation.

Glucosamine should be used with care by patients also taking warfarin.

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